Electrolytic preparation of olefin oxides



United States Patent 3,394,059 ELECTROLYTIC PREPARATION OF OLEFIN OXIDES Donald C. Young. Fullerton, Califi, assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Filed June 19, 1964, Ser. No. 376,583

7 Claims. (Cl. 20478) ABSTRACT OF-THE DISCLOSURE The invention comprises the electrolytic oxidation of olefins to olefin oxides in a diaphragmless electrolytic cell. In one embodiment, the electrolyte contains a soluble bromide which achieves maximum yields of the olefin oxide. In another preferred embodiment, the cathode comprises a pool of mercury which aids in maintaining the proper pH conditions for the oxidation of the olefin. The reaction is performed at temperatures from 25 to 300 C. and a sufiicient pressure to maintain liquid phase conditions. The olefin is introduced into the electrolyte while a direct current voltage is applied between the electrodes. The product can be removed continuously by vaporization from the electrolytic cell or a portion of the electrolyte can be withdrawn and distilled to recover the desired product.

This invention relates to a process for the production of olefin oxides; and in particular, relates to the production of olefin oxides by electrolytic oxidation.

I have found that hydrocarbon olefins having 2 to 10 carbon atoms can be electrolytically oxidized to valuable epoxides in attractively high yields by contacting the olefins with an electrolyte containing a soluble hydroxy compound and a soluble halide while applying a voltage thereto to induce current flow through said electrolyte.

In its simplest embodiment, my invention comprises preparing olefin oxides in a diaphragmless electrolytic cell comprising a vessel having cathodic and anodic elec' trodes by applying a voltage across said electrodes to induce an electric current flow through an electrolyte Whichcontains a soluble hydroxy compound and a soluble halide while contacting hydrocarbon olefins having 2 to 10 carbon atoms with said electrolyte to oxidize the olefins to epoxides. In its preferred form, my invention comprises using an aqueous electrolyte which contains a soluble' bromide salt, andin its most preferred form, a pool of mercury is used as a cathode for the electrolytic cell.

Hydrocarbon olefins that can be oxidized in accordance with my invention are branched or straight-chain unsaturated acyclic or cyclic olefins having one or more double bonds. Examples of such olefins are: ethylene, propylene, l-butene, Z-butene, n-pentene, cyclohexene, heptene, cyclooctene, octene,cyclononene, l-nonene, isodecene, etc. In general, olefins containing 2 to 10 carbon atoms can be oxidized by my method with the most preferred range being 2 to 5 carbon atoms. It is also within the scope of my invention to oxidize olefin mixtures, e.g., a mixture of propylene and l-butene, propylene and ethylene, etc.

Appropriate electrolytes'for use in my invention are aqueous electrolytes, i.e., having water as the solvent, and non-aqueous electrolytes, i.e., having an organic solvent as the major liquid component, which contain sufiicient quantities of dissolved salts to impart electric conductivity-Liquid organic hydroxy compounds having 1 to carbon atoms and preferably 1 to 5 carbon atoms or mixtures of. such liquid organic hydroxy compounds with water. or. withother organic'solvents comprise the preferred organic solvents that can be used as electrolytes.

In general, the following liquid organic hydroxy compounds can be used: alcohols such as methyl, ethyl, npropyl, iso-propyl, butyl, amyl, hexyl, octyl, decyl alcohols; ethylisopropylcarbinol, triethylc arbinol, phenol, furfuryl, cyclohexanol, heptan-Z-ol, diacetone alcohol, decan-l-ol, etc; glycols such as ethylene glycol diethylether, ethylene glycol monoethylether, ethylene glycol mono-iso-propylether, monomethyl glycol acetate, monoethyl glycol acetate, ethylene glycol mono-n-butyl-ether, glycol diformate, glycol, diethylene 'glycolmonomethylether, ethylene glycol dibutyl ether, triethylene glycol, etc.; low molecular weight aliphatic acids such as formic, acetic, propionic, butyric, valeric, etc.; and water. When an organic solvent in combination With a hydroxy compound is used, it is preferred to employ mixtures having from 0.1 to 50 weight percent and preferably, 1 to 10 weight percent hydroxy compound.

In general, any organic compound that is a liquid and chemically nonreactive with the olefin and the oxidation product at the reaction conditions can be used in combination with any of the aforementioned organic hydroxy compounds. Preferably an organic liquid having a solubility for the olefin is used. Examples of suitable solvents are: aromatic hydrocarbons such as benzene, toluene, xylene, etc.; aliphatic hydrocarbons such as hexane, heptane, iso-octane, nonane, decane, cyclohexane, methylcyclohexane, etc.; esters such as methyl acetate, ethyl acetate, dimethyl pthalate, ethyl propionate, n-propyl acetate, n-butyl formate, n-butyl acetate, iso-butyl acetate, iso-amyl acetate, cyclohexyl acetate, etc.; amides such as N,N-methylformamide, N,N-dimethylacetamide, formamide, etc.; and dimethylsulfoxide, methyl cyanide and fu-rfuran.

Inorganic hydroxide compounds that are soluble in the organic or aqueous electrolytes can also be used in my process. Examples of such compounds are: alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, etc.; alkaline earth hydroxides such as calcium hydroxide, strontium hydroxide, barium hydroxide, etc.; and ammonium hydroxide. The hydroxide compounds should be at least partially soluble in the electrolyte, i.e., a solubility of about 1 to 50 percent and preferably about 5 to 20 percent, and is employed at these concentrations.

The electrolyte contains a halide compound that is at least partially soluble in the electrolyte, i.e., a solubility of about 1 to 50 percent and preferably about 5 to 20 percent. The compound can be present as an elemental halide, e.g., chlorine, bromine, etc. However, it is preferred to use inorganic halides such as hydrogen halides, e.g., hydrogen chloride, hydrogen bromide, etc.; alkali metal halides, e.g., sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, lithium chloride, lithium bromide, lithium iodide, etc.; alkaline metal halides, e.g., calcium chloride, calcium bromide, barium chloride, barium bromide, barium iodide, magnesium bromide, magnesium chloride, magnesium iodide, etc.; transitional metal halides, e.g., cobalt bromide, cobalt chloride, cobalt iodide, iron bromide, iron chloride, nickel bromide, nickel chloride, nickel iodide, copper chloride, etc.; noble metal halides, e.g., palladium chloride, palladium bromide, platinum chloride, platinum bromide, etc. Organic halides which liberate hydrogen halide, halide ion or halogen under reaction conditions can also be used such as aliphatic halides, e.g., propylchloride, ethylbromide, carbon tetrachloride, methylbromide, heptylbromide, iso-amylbromide, iso-amylchloride, trichloropropane, pentachloroethane, iso-butylchloride, etc. The halides should be present in amounts from about 1 to weight percent and preferably from about 5 to 20 weight percent. It is also within the scope of my invention to use halide mixtures, e.g., a mixture of sodium bromide and potassium chloride.

Olefin oxides, are the major product of my oxidation method. However, the halide in the electrolyte tends to halogenate the olefin to a limited degree. I have discovered, that this tendency to halogenate the olefin can be substantially eliminated by use of a bromide as the halide in the electrolyte. Accordingly, I prefer to use any of, the aforementioned bromides as the soluble halide in the method of my invention, and most preferably, alkali metal bromides.

A suitable salt can also be added to the electrolyte to increase its electrical conductivity. In general, soluble alkali metal, alkaline earth metal and ammonia sulfates, sulfides, ch-romates, phosphates and carbonates can be used. Examplesof such salts are: sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, calcium sulfate, etc.; sulfides such as sodium sulfide, potassium sulfide, lithium sulfide, etc.; nitrates such as sodium nitrate, calcium nitrate, potassium nitrate, lithium nitrate, etc.; chromates such as potassium chromate, sodium chromate, potassium dichromate, lithium chromate, lithium dichromate, calcium chromate, etc.; phosphates such as sodium orthophosphate, sodium pyrophosphate, etc.; carbonates such as potassium carbonate, sodium carbonate, lithium carbonate, etc. The soluble salts can be used in amounts from about 1 to 50 weight percent and preferably, 5 to weight percent.

The process may be conveniently carried out in a diaphragmless electrolytic cell. The anode and cathode of the cell may be any material having good electrical conductivity such as platinum, gold, iron, steel, silver, nickel, copper, cadmium, tin, lead, mercury, zinc, carbon graphite, etc., and mixtures of these materials. While any of these materials can be used, I prefer to use a pool of mercury as the cathode. Because of the high hydrogen overvoltage of mercury, i.e., the difference between thepotential at which hydrogen gas is first produced from an electrolyte containing water and the theoretical reversible potential of the electrode in the same electrolyte, an additional reaction takes place at the cathode which initially lowers the pH of the electrolyte. For example, when an alkali metal halide such as sodium bromide is present in the electrolyte, sodium ions are discharged at the cathode which react with the mercury to form a sodium amalgam.

As the oxidation reaction progresses, theelectrolyte becomes basic. In a preferred method for controlling the pH, the amalgam concentration in the electrolytic cell is maintained constant at a predetermined value by periodic removal of said amalgam from the cell. In this manner, the pH of the electrolyte can be maintained at about 2 to 12 during the reaction and most preferably at about 8 to 10. At these controlled pH values for the electrolyte, halogenation can 'be substantially eliminated. It is also within the scope of my invention to periodically cycle the pH of the electrolyte during the reaction between about 3 and 11 by controlling the amalgam concentration in the cell in the aforementioned manner. When materials other than mercury are used for the cathode, it is desirable to control the pH of the electrolyte by the addition of an acid such as sulfuric, hydrochloric, nitric, phosphoric, acetic, etc.

The temperature of the electrolyte should be maintained at about to 300 C. and preferably about 10 to C. during the course of the reaction. This may be accomplished by any conventional means such as by immersing heat exchange surfaces in the electrolyte or by pumping the electrolyte through an external heat exchanger. Pressures from about one atmospheric to 1,000 p.s.i. and preferably, from about 50 to 200 p.s.i. can be used. Pressures above atmospheric pressure are preferred to obtain maximum solubility of the olefin in the electrolyte and retain the liquid phase.

Olefin oxidation can be performed in accordance with my invention in a batch or continuous process. The batch method is particularly suited for oxidation of normally liquid olefins, such as octylene, nonylene, etc. However, this method is not restricted to the use of such normally liquid olefins nor must these olefins be oxidized in a batch method. In this method, an electrolytic diaphragmless cell fitted with a thermometer and mechanical stirring means is charged with an electrolyte which contains a soluble. hydroxy compound, a soluble halide and an olefin. Electric current suflicient to oxidize the olefin is thenpassed through the cell. The electrolyte is maintained at a high electrical conductivity and only low voltages are needed for a current flow. During the oxidation reaction, a constant voltage can be maintained be tween the electrodes to induce continuous current flow through the electrolyte in one direction or the voltage can be periodically reversed, i.e., the cathode becomes the anode and the anode becomes the cathode, to reverse the direction of current flow through the electrolyte. By reversing the current flow, electrode polarization is eliminated.

Prior to complete oxidation of the olefin in the cell, the current flow is discontinued and the oxidation product is removed. To facilitate removal of the product from the electrolytic cell, a sweep gas, e.g., nitrogen, carbon dioxide, methane, ethane, etc., or any other gas which is inert to oxidation, can 'be used to strip the oxidation product from the electrolyte, if desired. While current is flowing through the electrolyte, it is desirable to maintain an excess of the olefin in the cell to prevent further oxidation of the epoxide to form esters, ethers, etc. The oxidation product can be recovered from the electrolyte by conventional separation means such as distillation which allows the electrolyte to be used again in subsequent reactions.

In the continuous method, the olefin is continually introduced into the electrolytic cell while the oxidation product is removed therefrom. This method is particu- -larly suited for the oxidation of a normally gaseous olefin such as ethylene and propylene. These olefins can be bubbled through the electrolyte and their oxidation product removed as a gas or liquid. As previously mentioned, when a mercury cathode is used in the electrolytic cell, it is desirable to remove the amalgam that forms in the cell to thereby maintain the electrolyte pH constant at the aforementioned values. This is accomplished by periodically or continually withdrawing a portion of the mercury from the cell and replacing it with a fresh supply of elemental mercury. The removal of the oxidation product can be facilitated with the use of a sweep gas to strip the product from the electrolytic cell. Unreacted olefins which are removed from the cell are separated from the oxidation product and recycled through the electrolytic cell. As in the case of a batch process, the temperature of the electrolyte can be controlled by conventional means and the reaction mixture can be stirred with a mechanical stirrer while the reaction is in progress.

The yield of hydrocarbon olefins to epoxides according to the method of my invention is about percent when operating at the preferred conditions previously discussed. In the continuous method of my invention, high epoxide conversion per olefin pass through the electrolytic cell are obtained, which make my process commercially desirable.

The following examples will illustrate the mode and practice of my invention and demonstrate the results obtainable thereby. I

Example I A three-liter flask was fitted with a stirrer, thermometer, gas delivery tube, product removal tube, and two /s-inch. diameter carbon rods for electrodes. The gas delivery tube was connected to a supply ofpropylene and the product removal tube was connected to a Dry Ice trap. The flask was charged with an electrolyte solution which contained 2,250 grams water and 250 grams potassium bromide. Propylene was bubbled through the solution and off gas was collected in the Dry Ice trap while a direct current voltage of 5 volts was impressed across the electrodes causing a current of about 1 ampere to flow through the solution. The current flow was maintained for two hours during which time the solution was maintained at about 5055 C. and at a pH of about 6.5 to 7.5. The electrolyte was then separated from the oxidation reaction product by distillation and the oxidation product was determined to be 97 percent propylene oxide.

Example II The procedure of Example I was repeated with the exception that the application of voltage between the electrodes was reversed every three minutes, i.e., the anode became the cathode and the cathode became the anode, causing the current flowing through the electrolyte to be reversed. The oxidation product was 87% propylene oxide.

Example III The apparatus described in Example I was used in this experiment with the exception that a platinum anode and a cathode comprising a pool of mercury one inch deep in contact with a platinum wire were used rather than the carbon electrodes of Example I. The electrolyte solution contained 250 grams sodium chloride and 2,250 grams water. Propylene was bubbled through the solution :and the off gas was collected in the Dry Ice trap. A direct current voltage of about 4.7 volts was impressed across the electrodes causing a current of about 1 ampere to flow through the solution. The current flow was maintained for 13 hours. The pH of the solution was initially 7.5; however, it varied in the following manner:

Time (hrs) HH NPWQVPHQ OIQNWWOJQO H pwpemees oocccucacoc Example IV The method of Example III was repeated with the exception that the cell was charged with 2,250 grams water and 250 grams sodium bromide. The oxidation product was 98 percent propylene oxide. The use of sodium bromide resulted in an increased conversion to propylene oxide of about 50 percent.

Example V The method of Example IV was repeated using ethylene as the hydrocarbon olefin instead of propylene. The oxidation product was 89 percent ethylene oxide.

The preceding examples are intended solely to illustrate my invention and are not to be unduly limiting thereof. My invention comprises the ingredients and steps or obvious equivalents thereof, set forth in the following claims.

I claim:

1. The method of preparing olefin oxides in an electrolytic cell having :a cathode and anode in open communication through a common electrolyte, which method comprises employing as said electrolyte an aqueous solution containing from 1 to about weight percent of a soluble bromide selected from the class consisting of soluble alkali metal, alkaline earth metal and transition metal bromides; impressing a direct current voltage between the anode and cathode to induce current flow through the electrolyte; and contacting the electrolyte with a hydrocarbon olefin having from 2 to about 10 carbon atoms while maintaining the temperature of the electrolyte at between -25 and 300 C. and the pressure sufficient to maintain the electrolyte in liquid phase at said temperature to oxidize said olefin to an olefin oxide.

2. The method of claim 1 wherein the hydrocarbon olefin is propylene.

3. The method of claim 1 wherein the soluble bromide is sodium bromide.

4. The method of claim 1 wherein the cathode of said electrolytic cell comprises mercury.

5. The method of claim 4 wherein the soluble halide is a soluble bromide.

6. The method of claim 4 wherein the hydrocarbon olefin is propylene.

7. The method for preparing olefin oxides in an electrolytic cell containing a single common electrolyte comprising an aqueous solution of from 1 to about 80 weight percent of a soluble alkali metal halide, the method that comprises: providing a pool of mercury and an electrode in said cell, applying an electronegative direct current potential to said pool of mercury relative to said electrode to induce current flow through said electrolyte; and contacting the electrolyte with a hydrocarbon olefin having from 2 to about 10 carbon atoms while maintaining the temperature of the electrolyte at between -25 and about 300 C. and the pressure sufiicient to maintain the electrolyte in liquid phase at said temperature to oxidize said olefin to an olefin oxide.

References Cited UNITED STATES PATENTS 1,253,617 1/1918 McElroy 204-80 1,308,797 7/1918 McElroy 204-80 1,992,309 2/1935 Hultman 20480 2,978,392 4/l96l MacLean et al. 20459 3,288,692 11/1966 Leduc 20480' JOHN H. MACK, Primary Examiner.

HOWARD M. FLOURNOY, Assistant Examiner. 

